It happens.
Sometimes life happens and partners may be forced to drop games without word.
Sometimes interest just unwaves and things hit a rut.
Sometimes people feel pressure in keeping up or don't have enough to properly work with for a reply and find themselves in a 'locked' state to keep the RP progressing.
Sometimes a person may feel like they are the one doing all the work.
Honestly there are many reasons of ghosting. I had people ghost in discussions. I had people ghost in RPs. Hell I been guilty of it as well years ago.
So what makes a RP and prevents the possibility of ghosting in happening?
Chemistry.
Well, players have to share similar tastes and personas. This is a hard given, I often make sure to see on F-List, Kinks, or something else and even inquire ahead of time. Plus players have their own standards as far as writing goes, character control goes, so on and so forth. Obviously it is best if partners can come to an agreement in what they want as oppose to just going with it. In truth, I rather have nothing transpire if me and a partner can't fully meet eye to eye than a partner just going with it and feeling dragged into a RP that they may not ultimately want to do.
Dedication.
Partners have to be dedicated in what they are to write. One person should not really be shoehorning everything. I know there may be those partners out there that would prefer for their partner to take control; but still. But still. Even I find it boring if partner is just going along for the ride; it just shows a lack of full dedication involving the setting, story, and whatever characters involved.
Cooperation.
RP is a team effort. One person cannot be the driving force behind it alone. Feedback is also important thing to keep a story interesting. I am not saying you have to radio all intentions in a play as elements of surprise are also one of the key factors; but players should have a general direction of where they are going with a game and be able to still freely discuss in what they want to include or how they like to progress(even if options.)
Patience.
Again there is often no telling what is going on. People shouldn't prod others repeatedly about a RP they may be involved with, with that person. There is always possibility that life is happening and that individual is too busy. The worst that may happen is if they indeed ghost. It sucks, it happens, but really nothing much to get work over of or about. RP is a hobby, its not life or at least for me.